[ x[20] = piecewise(t < -1, 0, t < 0, 0, t < 120, 1, 1),
  x[21] = x[20]*k[35],
  x[22] = x[1],
  x[23] = x[2],
  x[24] = x[3],
  x[25] = x[4],
  1*k[51]*x[1] + 1*k[51]*x[2] + 1*k[51]*x[3] + 1*k[51]*x[4] + 1*k[51]*x[5] + 1*k[51]*x[7] + 1*k[51]*x[8] + 1*k[52]*x[9] + 1*k[52]*x[10] + 1*k[52]*x[11] + 1*k[52]*x[12] + 1*k[52]*x[13] + 1*k[52]*x[15] + 1*k[52]*x[16] + 1*k[52]*x[17] = k[51]*k[53] + k[52]*k[54],
  1*k[51]*x[6] + 1*k[51]*x[7] + 1*k[51]*x[8] = k[51]*k[55],
  1*k[52]*x[14] + 1*k[52]*x[15] + 1*k[52]*x[16] + 1*k[52]*x[17] = k[52]*k[56] ]